The present invention relates generally to agricultural implement frames and more specifically, to lift and leveling systems for such frames.
Agricultural implement frames for pull-type implements such as tillage and seeding equipment or the like typically include a level lift rockshaft system. A rear-mounted rockshaft weldment connected to lift wheel assemblies is mechanically linked through a complex linkage arrangement to a hitch pivotally connected to the front of the frame. A bellcrank is connected through a link to the hitch. As the rockshaft is rotated to change the position of the lift wheels relative to the frame, the implement is raised and lowered and the linkage arrangement pivots the hitch to maintain the frame in generally a level condition.
Most level lift rockshaft systems have a relatively large number of parts and wear points. As a result, such systems are usually heavy and expensive. A large number of wear points make such a system somewhat unreliable. The conventional aft location of the heavy rockshaft structure detrimentally shifts considerable weight to the rear of the implement. Torsional windup of the rockshaft is also a common problem, and the rockshaft must have a substantial wall thickness to withstand the torsional forces and prevent windup, a requirement which adds to the weight and expense of the implement. The rockshaft is subject to extreme shock loading, particularly when the implement is fully raised to a transport position.
It is therefore an object of the present invention to provide an improved rockshaft system for an implement. It is another object to provide such a system which overcomes most or all of the aforementioned problems.
It is a further object of the invention to provide an improved rockshaft system for an implement which is less expensive to manufacture, more reliable in operation and more advantageous in weight distribution than at least most previously available rockshaft systems. It is another object to provide such a system which has reduced rockshaft windup, less complex mounting and linkage structure and fewer wear points.
It is a further object of the invention to provide a relatively low cost implement frame with an economical level lift rockshaft system, better weight and load distribution, and fewer wear points than at least most previously available implement frames.
A rockshaft is mounted over the front rank of the implement frame and operated by cylinders located at opposite ends. Each cylinder is connected to a lift arm extending radially from an end of the rockshaft which also is directly connected to a fore-and-aft extending link which operates trailing lift wheel modules connected to the frame. A hitch arm connected near the center of the rockshaft is directly connected to a hitch turnbuckle for level lift operation without need for a complicated bell crank structure. The use of the two end cylinders with direct coupling of the lift linkages facilitates use of a parallel/series type of hydraulic circuit with torsional forces resulting from the hitch leveling forces only. Three or more adjustably locatable sets of rockshaft bearing mounts connect the rockshaft to the front tube of the implement frame at locations substantially aligned with hitch and lift arms. The arrangement of cylinders, supports and arms provides minimal torsional loading, and therefore a thinner walled tube can be used to reduce cost and weight. When the rockshaft is rotated to fully raise the implement frame for transport and is in the most susceptible shock loading condition, the torsional loading is minimized, greatly reducing stress and improving the reliability of the frame and lift system. The reduced number of components, improved loading characteristics, and improved weight distribution provide a cost effective, strong and reliable implement frame.